(321c) Polystyrene Nanoparticles As a Model System to Investigate 3-Dimensional Confinement Effects On the Glass Transition Temperature

When confined to the nanoscale, the glass transition temperature (T_g) of polymers can deviate substantially from the bulk, in what is commonly referred to as the T_g-confinement effect.  Due to ease of processing, most studies have focused on the size-dependent T_g of thin films, while few have extended investigations to other geometries.  As polymers confined to higher geometrical dimensions become the enabling material in technologies ranging from drug delivery to plastic electronics, a greater understanding of size effects on the T_g  is warranted.  Here, we investigate the effect of soft and hard three-dimensional confinement on the T_g of polymer nanoparticles.  Via modulated differential scanning calorimetry, we show that the T_g can decrease significantly with size for aqueous suspended polymer nanoparticles, i.e., the case of soft confinement. Furthermore, capping of the nanoparticles with a silica shell leads to a size-invariant T_g, i.e., the case of hard confinement.  Lastly, using a unique flash nanoprecipitation method to generate polymer nanoparticles of the same size but different molecular weights, we examine the impact of polymer molecular weight on the T_g of 3-dimensional confined polystyrene nanoparticles.